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Thursday, May 10, 2012

Diesel Engine Inframe Rebuild, Part 2

For a complete guide on rebuilding the DT466, click on the book sales tab above this post.
Hello, and welcome to part 2 of the DT466 inframe service. Last time we tore down the engine, and now it is time to inspect parts and clean everything up.Cleanup actually starts with a close inspection of all the parts taken off. It goes without saying that you need to keep track of where parts came from so that rods, cam followers, and pushtubes go back in their original positions, and so that you can track down the cause of a damaged part. The injectors need to be checked for evidence of damage, leaks, or overheating, especially the lower end. Also see that the metal nozzle seal stayed on the end of the injector and is not stuck down in the bottom of the cup. The head must be checked for leaks, cracks, and any flaw that could cause a problem, especially in the injector bores. Checking valve seal was covered in part 1, and the injector cups must also be checked for leaking. The injector cups are in contact with the engine coolant and serve to cool the ends of the injectors. It is not uncommon to pull an injector and find the cup has leaked coolant onto the end of the injector. In the 466, the cups are press fit into the head. Although removing and replacing them is not difficult, it does require special tools. The injector bores must be closely inspected for any damage or signs of contamination. All cam followers must be removed from the block and the roller ends, guides, and cam lobes checked for wear and damage from above and below, or by turning the crankshaft. The dog bone cam follower guides are a weak part on this engine. One will occasionally break and allow its pair of cam followers to turn sideways, quickly taking out the pair of cam lobes. The authorized fix for the problem is to use 2 guides on each pair of followers.Rod bearings need to be checked for unusual wear patterns such as edge wear indicating a bent rod, and pistons for damage and overheating. And overheated piston can be caused by lack of coolant, low coolant flow, or a failed piston oiler. Rocker shaft assembly inspection was covered earlier, but the pushtubes need to be checked for straightness and damaged ends.In addition to checking the cam, the block assembly needs to be checked for any damage or evidence of leaking or overheating. The liner counterbore and bottom seal bore must be very carefully checked and cleaned to prevent problems down the road. Also check the deck surface before and as it is cleaned.

As for cleaning up parts, there are three areas I spend extra time on; the liner counterbore and seal area mentioned before, the deck surface, and the head and high pressure oil rail mating surfaces. It is worthwhile to spend lots of time on the counterbores and deck, as this directly affects durability and freedom from leaks. I spend whatever time it takes to get the bottom of the counterbores perfectly clean. I never clean them with anything but a Scotchbrite pad and elbow grease. I look at the counterbores from both sides and use a mirror, if needed, to ensure they are perfect. If anything is left stuck to this surface you cannot properly measure the liner protrusion, and that is one thing that absolutely must be to spec on a diesel engine. I do use a screwdriver to scrape carbon from the vertical counterbore surface, but I don’t get too aggressive. The lower liner seal surface where the O-rings seal must also be cleaned thoroughly. As for the block deck, I use a fine Roloc disc on a 90 degree die grinder, but use a light touch and do not grind down any corners or edges. Remove the chunks and tightly stuck pieces of head gasket, then go to Scotchbrite and more elbow grease. It is not at all unusual to spent 2 hours or more just in cleaning the counterbores and deck. As for the high pressure oil rail, always replace the beaded metal gasket, as they are prone to leaking. Again, I never use anything but Scotchbrite pad where the beads of the gasket seal on the rail and the head. Any nick or low spot will guarantee a leak at 3000-5000 psi of oil pressure.

Liners are dropped in
to check protrusion.
Bolts clamp one liner
at a time for measurement.

Liner protrusion measurement
must meet manufacturers
specifications.

After cleaning the deck surface I usually run a tap down all the headbolt holes (and the exhaust manifold threads in the head), then blow all the coolant, oil, and junk out of them. Wipe everything down and take a last look to see that no dirt or pieces of gasket have fallen onto the counterbores. Number the liners and slide them into the block without O-rings.

The liners must be clamped to simulate the head being installed, then the protrusion is checked with a dial indicator. The protrusion spec for this engine is .002 - .005”. The narrow range of this specification is why we need to be so careful in cleaning the counterbore surface that the liner fits to. Liner protrusion provides the proper amount of crush on the head gasket fire ring. Too much protrusion and the engine may develop a leaking head gasket, while too little protrusion or a sunk liner will not contain combustion chamber pressure. Any cylinder that doesn’t meet the specification must have a shim installed or, very rarely, have the counterbore cut deeper. It is very rare to find a 466 with a problem in this area, although you may occasionally need to exchange a liner with a high dimension with another that measures lower. After the protrusion is verified, the liners can be pulled out and fitted with the lower seals. These are lubricated and the liners slid into place. They must be seated with a deadblow hammer or a block of wood and a heavy hammer, then clamped down for a few minutes until the seals relax. If they aren’t clamped down, they will pop back up after a minute.This is about the end of day 2 in our inframe service, so check back soon for part 3 where we finish assembly and fire up the new engine.